US2512596A - Production of alkenyl thiophenes - Google Patents

Description

Patented June 27, 1950 I PRoDUoTroN or ALKENYL THIOPHENES Delaware f llol rawing. ,dpplication August 1, 1946, Serial N0. 687,702 I '13 Claim s; 7 (01. 260-329) f The present invention relates to the'production of jallgenyl thiophenes. In one of its morespec ific aspects the present invention relates to the production of alkenyl thiophenes by the reaction of an alkylpthiophene with formaldehyde. The process or the' present invention is particularly useful, for the production of 2-vinylthiophene from thiotolene'and'formaldehyde.

Alkenyl thiophenes have many. potential uses in the chemical industryand would find wide appli cation if. readily available. 2-vinylthiophene iii-particular is potentially valuable a's a comonomerin the polymerization of'vinyl compounds for the production of synthetic rubber. The extensive use of 2- vinylthiophenefor the production oi high molecular weight'polymers of a rub-. bery or resinous nature depends to alarge extent upon the quantit'yjproduction of vinylthiophene by an 'efiicientand economical process. Vinyl thiophenes have other potential uses,"particularly as'intermediates in the production of sulfur-containing chemicals, and other uses which will be apparent to those skilled in the art.

The process of the. present'invention provides a means'for the large'scale production of alkenyl thiophenes efficiently and economically. In accordance with 'this invention an (alkyl thiophene is reacted with formaldehyde under controlled reactioncdiiditidri's to produce alkenyl thiophenes. For the production of- 2-vinylthiophene, thiotolene (2f-methylthiophene) is reacted with formaldehyde. Monomethylol-Z-thiotolene is also produced by "the reaction of formaldehyde with 2- methylthiophene in accordance with this invention and may,-if desired, b'e recovered as one of the products ofg theprocess. The process is preferably conducted in a continuous manner as hereinafter more fully described." The conversion of--alkyl thiophenes to alkenyl thiophenes isefiected in the presence of a catalyst, preferably in a single step.. Alkenyl'thiophenes have been previously prepared by various methods and are recorded in the literature. These include 2- vinylthiophene 2-.ally1thiophene,. 2-.(alphaeth- 1 ylpropenyD-thiophene, and 2-isopropenylthiophene.:-= 2-vinylthiophene has been, prepared by Alkenyl thiophenes may be prepared by a much more economical and direct method in accord-; ance with the present invention. K

An object of the present invention is to provide an improvedprocess for the production'of alkenyl thiophenes. A further object of the present invention is to provide a process for the production of alkenyl thiophenes from alkyl thiophenes and formaldehyde. Anotherobject of the present invention is ,to provide an improvedprocess for the production of z-vinylthiophene and'its homologs. It is anotherobject of the present invention to provide a continuous process for the production. of alkenyl thiophenes from alkyl thiophenesand I formaldehyde by the simultaneous condensation of the alkyl thiophenes with formaldehyde anddehydration to produce alkenyl thiopenes 0th.-

er objects and advantages of the invention-some of which are referred to specifically hereinafter, in the art to} will be apparent to those skilled which the invention pertains I The production of alkenyl thiophenes the :2 interaction of alkyl thiophenes and formaldehyde L involves two reactions, the addition of formalde hyde to an alkyl thiophene to form the corresponding monomethylol derivative of the alkyl thiophene and dehydration of the monomethylol derivative of the alkyl thiophene to the alkenyl thiophene.

phene by this method the reactions involved are Ho- 'oH H -OHr-OHuOH s Homologs of vinyl thiophene, e. g'., alkyl sub stituted vinyl thiophenes, may be produced in a similar manner. ethylthiophene may be converted to 2-vinyl- 5- ethylthiophene by formation of the monomethylol derivative and subsequent dehydration to 2 'vinyl-5-ethylthiophene." Qther homologs of vinyl thiophene may be produced in an analogous" manner.

The present invention provides an improved process for the production of vinyl thiophene, its homologs and derivatives from an alkyl, thioj phene containing the alkyl group attached to a. carbon atom in the thiophenenucleus in the 2': position, as exemplifiediby the "foregoing reac 1 tions. Thiophene derivatives employedinarid,

In the production of 2-vinylthio- As an example, 2-methyl-5-- produced by the process may also contain chloro or cyano substituents, or both, attached to a carbon atom in the thiophene nucleus. The present invention is particularly applicable to the production of 2-vinylthiophene from 2-methylthiophene and formaldehyde. The intermediate monomethylol derivative of the alkyl thiophene may be separately recovered, if desired, and dehydrated to the alkenyl thiophene in a separate step or recycled to the reaction together with the alkyl thiophene and formaldehyde feed.

The present invention provides a novel process for the production of alkenyl thiophenes. While various alkyl thiophenes containing an alkyl group attached to a carbon atom in the 2-position and referred to herein as z-alkylthiophenes, may be employed as starting materials for the present process, the preferred alkyl thiophenes are those having an alkyl group containing from 1 to 6 carbon atoms attached to a carbon atom in the 2-position in the thiophene nucleus to produce the corresponding alkenyl thiophenes having one additional carbon atom in the alkenyl group. My novel process is carried out inthe vapor phase-in the presence of catalysts which are particularly effective for this reaction. By the process of my invention new alkenyl thiophenesand their derivatives may be produced. The process is adapted to smooth, continuous operation without substantial interference from polymeric Icy-products.

In accordance with the present invention the alkyl thiophene is admixed with formaldehyde and passed in vapor phase at an elevated temperature into contact with a catalyst. The molecular proportions of formaldehyde and alkyl thiophene are preferably within the range of from about 0.5 to about 1 mol of formaldehyde per mol'of alkyl thiophene. The efiiuent' comprises the alkenyl thiophene, unchanged reactants, and the monomethylol alkyl. thiophene intermediate. The effluent is subjected to fracti'onal distillation to effect the separation of the product from the other components of the mix ture.

The formaldehyde may be either in anhydrous form or in an aqueous solution. Dilute aqueous solutions of formaldehyde, such as the 37' per cent solution of. commerce, are suitable for use in the processof the present invention. Formaldehyde used for this reaction may be added in an aqueous solution, as paraformaldehyde, or as trioxane with equally good results. When paraformaldehyde is used, water may be added to facilitate separation of unchanged reactants for recycling.

The preferred catalysts for use in the process of the present invention are relatively non-volatile strong mineral acids (1. e. sulfuric acid and phosphoric acid) ,anhydrides of these acids, and acid reacting salts of these acids. Phosphoric acid, sulfuric acid, and potassium persulfate are particularly effective. Preferably the relatively non-volatile strong mineral acid, anhydride, or acid reacting salt is supported on a dehydrating metal oxide. The dehydrating metal oxides comprise alumina, bauxite, silica gel, silica-alumina gel and other mixed oxides of silicon and aluminum, such .as fullers earth, attapulgus clay, Floridin earth, and the like. Other dehydrating metal oxides may be used, e. g., oxides. of thorium, tungsten, vanadium and molybdenum but are not generally commercially economical. The catalyst may be prepared by impregnating the dehycrating metal oxide, preferably in granular or pellet form, with a solution of the acid component, i. e., the relatively non-volatile strong mineral acid, anhydride of a relatively non-volatile strong mineral acid or an acid reacting salt. The acid component of the catalyst has an ailinity for water and is consequently present on the carrier in an aqueous solution during operation. The concentration of the aqueous solution of the acid component may be controlled by control of the quantity of water vapor in the feed stream. The preferredrange of concentration for sulfuric acid is to 100 per. cent and for phosphoric acid 60 to 100 per cent; Acid concentrations of per cent orthophosphoric and per cent sulfuric are especially suited to the present process. Anhydridesof these acids, e. g., phosphorous pentoxide and sulfur trioxide, and alkali metal strong acid reacting salts of these acids, particularly sodium dihydrogen phosphate and potassium persulfate are effective catalysts for the reaction. The anhydrid'es are rapidly diluted with water due to the dehydration reaction. Boron trifluoride and alkali fluoborates, e. g,, sodium fluoborate and potassium fluoborate are also effective catalysts for the reaction. While the re' a c tion will proceed to some extent in the absence of a catalyst, the above-mentioned catalysts give definitely higher yields of the desired product than do non-catalyzed operations; Orthophosphoric acid and potassium persulfate are selective in their actions and, make possible higher ultimate yields. Pellets of alumina, about. 5 inch in diameter and V; inch long, and granular silica-alumina gel are preferred as the dehydrating metal oxide carriers.

Temperatures employed for the process are in general. within the range of from about 200' to about 800 F., preferably from about300 to about 600 F. Pressure requirements are not critical. Satisfactory results are obtained in. the range of fromabout atmospheric pressure to. about pounds per square inch. Yields of, alkenyl thiophenes within the range of, 1.0 to 20per centper pass based on the alkylthiophene. charged may be obtained.

In a specific example of the operation of the process of this invention thiotolene (Z-methylthiophene) is admixed with formaldehyde in the ratio of about 3 mols of formaldehyde to .5 mols of thiotolene and the mixture preheated to a-temperatu-re within the-range of from about 400- toabout 450 F. The mixture, at a pressure of about 30 pounds per square inch gage,is passed into contact with a catalyst comprising about 5 Weight per cent orthophosphoric acid supported on granular silica-alumina gel; The effluent of the catalyst is condensed and separated by freetional distil-lation into aproduct stream ofsubstantially pure '2-Vil'lY1thiO10hBI1B and a recycle stream comprising unchanged reactants and monomethylolJ-thiotolene;

From. the foregoing, it is believed that the many advantages obtainable. from the practice of the. present invention-will be readily apparentzto personsski-lled in. the art. However, since certain changes may be made in carrying out theabove method without departing from the scope of the invention, as defined by the appended claims, it is intended that all matter contained herein shall be interpreted as illustrative and explanatory, rather than in a limiting sense.

I claim:

1. A process for the production of an .alkenyl thiophene which comprises. reacting a 2-,alkyl thiophene selected from the sroupconsistins 9,1"

unsubstituted 2-alkyl thiophenes, alkyl substituted 2-alkyl thiophenes, chloro substituted 2- alkyl thiophenes and cyano substituted Z-alkyl thiophenes wherein the substitution is on a nuclear carbon atom, with formaldehyde at a temperature within the range of from 200 F. to 800 F. and in the vapor phase in the presence of a catalyst comprising an acid component selected from the group consisting of relatively non-volatile strong mineral acids, anhydrides of said acids, and acid reacting salts of said acids.

2. A process as defined in claim 1 wherein said alkyl thiophene is 2-methylthiophene.

3. A process for the production of an alkenyl thiophene which comprises reacting a 2-alkyl thiophene selected from the the group consisting of unsubstituted 2-alkyl thiophenes, alkyl substituted 2-alkyl thiophenes, chloro substituted 2-alkyl thiophenes and cyano substituted 2-alkyl thiophenes wherein the substitution is on a nuclear carbon atom, with formaldehyde at a temperature within the range of from 200 F. to 800 F. and in the vapor phase in the presence of a catalyst comprising a relatively non-volatile strong mineral acid.

4. A process as defined in claim 3 wherein said acid is orthophosphoric acid.

5. A process for the production of 2-vinylthiophene which comprises reacting Z-methylthiophene with formaldehyde at a temperature within the range of from 200 F. to 800 F. and in the vapor phase in the presence of phosphoric acid as a catalyst.

6. The process which comprises the interaction of a 2-a1kyl thiophene selected from the group consisting of unsubstituted 2-a1kyl thiophenes, alkyl substituted 2-alkyl thiophenes, chloro substituted 2-alkl thiophenes and cyano substituted 2-alkyl thiophenes wherein the substitution is on a nuclear carbon atom, said 2-alkyl thiophene containing from 1 to 6 carbon atoms in the alkyl group, and formaldehyde at a temperature within the range of from 200 to 800 F. and in the vapor phase.

'7. The process which comprises the interaction of 2-methylthiophene with formaldehyde at a temperature within the range of from 200 F. to 800 F. and in the vapor phase in the presence of a relatively non-volatile strong mineral acid.

8. A process for the production of 2-vinylthiophene which comprises reacting 2-methylthiophene with formaldehyde at a temperature of from 200 to 800 F. and in the vapor phase in the presence of a catalyst comprising a minor proportion of phosphoric acid deposited on a solid granular dehydrating oxide.

9. A process for the production of 2-vinylthiophene which comprises forming a mixture of formaldehyde and Z-methylthiophene, passing said mixture in the vapor phase into contact with a catalyst comprising a minor proportion of phosphoric acid supported on silica-alumina gel at a temperature within the range of from 300 to 600 F.

10. The process which comprises the interaction of a 2-alkyl thiophene selected from the group consisting of unsubstituted 2-a1kyl thiophenes, alkyl substituted 2-alkyl thiophenes, chloro substituted 2-alkyl thiophenes and cyano substituted Z-alkyl thiophenes wherein the substitution is on a nuclear carbon atom, said 2-alkyl thiophene containing from 1 to 6 carbon atoms in the alkyl group, and formaldehyde at a temperature within the range of from 200 to 800 F. and in the vapor phase in the presence of a catalyst comprising boron trifluoride.

11. A process as defined in claim 6 wherein there are employed temperatures within the range of from 300 F. to 600 F., and mol ratios of formaldehyde to 2-a1kyl thiophene within the range of from 0.521 to 1:1.

12. A process as defined in claim 1 wherein said 2-alkyl thiophene contains from 1 to 6 carbon atoms in the 2-alkyl group, and wherein there are employed temperatures within the range of from 300 F. to 600 F., and mol ratios of formaldehyde to 2-alkyl thiophene within the range atoms in the alkyl group, and formaldehyde at a temperature within the range of from 200 to 800 F. and in the vapor phase in the presence of a catalyst comprising an alkali fiuoborate.

PHILIP M. ARNOLD.

REFERENCES CITED The following references are of record in the file of this patent:

J. S00. Chem. Ind. 49, 245.51 T (1930)

Claims (1)

1. A PROCESS FOR THE PRODUTION OF AN ALKENYL THIOPHENE WHICH COMPRISES REACTING A 2-ALKYL THIOPHENE SELECTED FROM THE GROUP CONSISTING OF UNSUBSTITUED 2-ALKYL THIOPHENS, ALKYL SUBSTITUTED 2-ALKYL THIOPHENS, CHLORO SUBSTITUTED 2ALKYL THIOPHENS AND CYANO SUBSTITUTED 2-ALKYL THIOPHENS WHEREIN THE SUBSTITUTION IS ON A NUCLEAR CARBON ATOM, WITH FORMALDEHYDE AT A TEMPERATURE WITHIN THE RANGE OF ROM 200*F. TO 800*F. AND IN THE VAPOR PHASE IN THE PRESENCE OF A CATALYST COMPRISING AN ACID COMPONENT SELECTED FROM THE GROUP CONSISTING OF RELATIVELY NON-VOLATILE STRONG MINERAL ACIDES, ANHYDRIDES OF SAID ACIDS, AND ACID REACTING SALTS OF SAID ACIDS.